Ratchet Effect Research Articles

Управление нанотранспортом с помощью рэтчет-эффекта

Управление нанотранспортом с помощью рэтчет-эффекта

Topologically protected superconducting ratchet effect generated by spin-ice nanomagnets

We have designed, fabricated and tested a robust superconducting ratchet device based on topologically frustrated spin ice nanomagnets. The device is made of a magnetic Co honeycomb array embedded in a superconducting Nb film. This device is based on three simple mechanisms: (i) the topology of the Co honeycomb array frustrates in-plane magnetic configurations in the array yielding a distribution of magnetic charges which can be ordered or disordered with in-plane magnetic fields, following spin ice rules; (ii) the local vertex magnetization, which consists of a magnetic half vortex with two charged magnetic Néel walls; (iii) the interaction between superconducting vortices and the asymmetric potentials provided by the Néel walls. The combination of these elements leads to a superconducting ratchet effect. Thus, superconducting vortices driven by alternating forces and moving on magnetic half vortices generate a unidirectional net vortex flow. This ratchet effect is independent of the distribution of magnetic charges in the array.

Asymmetric effects of financial dollarization on nominal exchange rate volatility in Nigeria

The paper investigates the relationship between financial dollarization and nominal exchange rate volatility in Nigeria. To achieve this objective, a Threshold Autoregressive Conditional Heteroscedasticity (TARCH) model using monthly data for the period December 2009 to September 2018. From the estimation results, it is evident that nominal exchange rate volatility in Nigeria is driven by the degree of financial dollarization, all things equal. It is also evidence from the study that exchange rate volatility exhibit high degree of persistence and ratchet effect. In other words, bad news of depreciation in the nominal exchange rate trigger foreign currency holding which further depreciates the domestic currency exchange rate more than the good news of appreciation lead to further appreciation of the nominal exchange rate of the domestic currency.

Skyrmion ratchet effect driven by a biharmonic force

Based on micromagnetic simulation and analysis of Thiele's equation, in this work we demonstrate that ratchet motion of skyrmion can be induced by a biharmonic in-plane magnetic field hx(t) = h1sin(mwt) + h2sin(nwt + phi), provided that integers m and n are coprime and that m + n is odd. Remarkably, the speed and direction of the ratchet motion can be readily adjusted by the field amplitude, frequency and phase, with the maximum speed being over 5 m/s and the direction rotatable over 360 degree. The origin of the skyrmion ratchet motion is analyzed by tracing the excitation spectra of the dissipation parameter D and the skyrmion position R, and it shows that the dissipative force plays a key role in the appearance of ratchet motion. Such a ratchet motion of skyrmion is distinguished from those caused by single-frequency ac drives reported in the literature, and from that driven by pulsed magnetic fields as also predicted in this work. Our results show that skyrmion ratchet effect under biharmonic forces shares some common features of those found in many soliton systems, and the facile controllability of both the skyrmion speed and direction should be useful in practice.

Movement of spherical colloid particles carried by flow in tubes of periodically varying diameter.

We provide analytical formulas for the movement of spherical particles in a corrugated tube, in the approximation of small amplitude of the tube diameter variation. We calculate how the particle is pushed toward the wall at some places and pulled off the wall at others. We show that this effect causes rectification of the particle movement, when the direction of the fluid flow is alternated, thus leading to the hydrodynamic ratchet effect. We propose such scheme as a particle-separation device.

High-temperature ratchets driven by deterministic and stochastic fluctuations.

We consider the overdamped dynamics of a Brownian particle in an arbitrary spatial periodic and time-dependent potential on the basis of an exact solution for the probability density in the form of a power series in the inverse friction coefficient. The expression for the average velocity of a Brownian ratchet is simplified in the high-temperature consideration when only the first terms of the series can be used. For the potential of an additive-multiplicative form (a sum of a time-independent contribution and a time-dependent multiplicative perturbation), general explicit expressions are obtained which allow comparative analysis of frequency dependencies of the average velocity, implying deterministic and stochastic potential energy fluctuations. For qualitative and quantitative analysis of these dependences, we choose illustrative examples for spatial harmonic fluctuations: with deterministic time dependences of a relaxation type and stochastic time dependences describing Markovian dichotomous and harmonic noise processes. We explore the influence of fluctuation types on the ratchet effect and demonstrate its enhancement in the case of harmonic noise.

On the clock of the combinatorial clock auction

The combinatorial clock auction (CCA) has frequently been used in recent spectrum auctions. It combines a dynamic clock phase and a one‐off supplementary round. The winning allocation and the corresponding prices are determined by the Vickrey–Clarke–Groves rules. These rules should encourage truthful bidding, whereas the clock phase is intended to reveal information. We inquire into the role of the clock when bidders have lexicographic preferences for raising rivals' costs. We show that in an efficient equilibrium, the clock cannot fully reveal bidders' types. In the spirit of the ratchet effect, in the supplementary round competitors extract surplus from strong bidders whose type is revealed. We also show that if there is substantial room for information revelation, that is, if the uncertainty about the final allocation is large, all equilibria of the CCA are inefficient. Qualitative features of our equilibria are in line with evidence concerning bidding behavior in some recent CCAs.

储氢床不锈钢疲劳寿命预测及棘轮效应和应变强化竞争机理描述

储氢床不锈钢疲劳寿命预测及棘轮效应和应变强化竞争机理描述

The Network Effects of International Financial Regulation

This paper examines the question of global coordination among financial regulators through the lens of network effects. It introduces and surveys three unique kinds of network effects which can be created by the adoption of a global financial regulatory standard: (a) network effects in the financial markets; (b) network effects among the regulated firms; and (c) network effects among the financial regulators themselves. This paper offers a model which shows that positive network effects can generate a spiral ratchet effect that will induce countries to sequentially adopt global financial regulatory standards.

Relative Performance Evaluation and the Ratchet Effect

ABSTRACTWhen targets depend on past performance, incentives are adversely affected by the ratchet effect. We provide theory and evidence that incorporating past peer performance into targets can alleviate this adverse incentive effect. In particular, we present an analytical model that characterizes optimal target revisions as a function of past own and past peer performance. We then test the predictions of our model using data on 2008–2010 performance targets from 354 units of a governmental agency responsible for reintegration of the long‐term unemployed into the labor market. As a unique feature of our data, we have information on peer group quality, defined as the extent to which peer performance is informative about common shocks. Consistent with our model, we find that higher peer group quality (a) increases sensitivity of target revisions to past peer performance, (b) reduces sensitivity of target revisions to past own performance, and (c) reduces the ratchet effect as reflected in managerial incentives to withhold end‐of‐year effort.

Feynman-Smoluchowski ratchet in an effective one-dimensional picture

A simple two-dimensional (2D) model of the Feynman-Smoluchowski ratchet is studied. Motion of the wheel, driven by stochastic hits of the surrounding molecules, is described as diffusion along the longitudinal coordinate $x$; the stochastic motion of the pawl is represented in the transverse coordinate $y$. Different temperatures of the reservoirs connected to the particular degrees of freedom, together with asymmetry of the energetic landscape of the system, give rise to the ratchet effect. We apply mapping of the corresponding 2D Fokker-Planck equation onto the longitudinal coordinate $x$. The mapped 1D equation is of the generalized Fick-Jacobs type with an effective potential containing a part increasing or decreasing with $x$, connected with vorticity of the scaled driving force and the stationary probability current. It is responsible for the final rectified motion in the longitudinal direction.

Constitutive mechanisms of UN Security Council practices: Precedent pressure, ratchet effect, and council action regarding intrastate conflicts

AbstractBased upon the current debate on international practices with its focus on taken-for-granted everyday practices, we examine how Security Council practices may affect member state action and collective decisions on intrastate conflicts. We outline a concept that integrates the structuring effect of practices and their emergence from interaction among reflective actors. It promises to overcome the unresolved tension between understanding practices as a social regularity and as a fluid entity. We analyse the constitutive mechanisms of two Council practices that affect collective decisions on intrastate conflicts and elucidate how even reflective Council members become enmeshed with the constraining implications of evolving practices and their normative implications. (1) Previous Council decisions create precedent pressure and give rise to a virtually uncontested permissive Council practice that defines the purview for intervention into such conflicts. (2) A ratcheting practice forces opponents to choose between accepting steadily reinforced Council action, as occurred regarding Sudan/Darfur, and outright blockade, as in the case of Syria. We conclude that practices constitute a source of influence that is not captured by the traditional perspectives on Council activities as the consequence of geopolitical interests or of externally evolving international norms like the ‘responsibility to protect’ (R2P).

Solution-Processed Ion-Free Organic Ratchets with Asymmetric Contacts.

Ion-free organic ratchets with asymmetric injecting contacts (AICs) are fabricated using solution-processable organic semiconductors. Scanning Kelvin probe microscopy analysis reveals that the rectifying function is achieved via the "charge pump" mechanism. Electrical characterizations show that the device can readily operate under industrial standard radio frequency and its high-frequency performance may be enhanced through further material/device engineering. The built-in asymmetric feature exempts the devices from the complicated material design, device processing, and performance decay associated with the use of ion/semiconductor blends in ionic-organic ratchets. Thus, the AIC ratchets can deliver a persisting ratchet effect and have excellent material compatibility toward organic semiconductors.

Plasmon ratchet effect with electrons and holes simultaneously existing in the graphene channel: a promising effect for the terahertz detection

In this work, the plasmon drag effect in the grating gated graphene with symmetric unit cell, the plasmon ratchet effect and the photo-thermoelectric effect in the grating gated graphene with asymmetric unit cell are studied. The correlation between the total responsivity of the plasmon drag effect and the source-drain bias is calculated numerically through the hydrodynamic approach under small source-drain bias approximation. The total responsivity of the plasmon drag effect under small source-drain bias is found to be much smaller than the responsivity of the unidirectional travelling plasmons. The responsivity of the plasmon ratchet effect is calculated by fixing the lengths of the longer gated region and ungated region and changing the lengths of the shorter gated region and ungated region. The results show that non-zero plasmon ratchet responsivity can be obtained by only assuming one kind of charge carrier in the whole channel. By assuming holes in the shorter gated region and electrons in the other regions, the maximum responsivity is much higher than the former and can be as high as that reported in the reference. The responsivity of the photo-thermoelectric effect can be higher than that of the plasmon ratchet effect for currently available graphene. For ideal graphene with ultrahigh mobility, however, the responsivity of the photo-thermoelectric effect is orders of magnitude smaller than that of the plasmon ratchet effect.

Police Transparency and the Exclusionary Rule

In the old days, police officers bent on misconduct went about their business with bankable allies. Colleagues could be counted on to lie under oath, prosecutors remained willfully blind, and when all else failed, judges and juries were prepared to grant an officer the benefit of doubt. But officers today work in a stricter environment, notable for both its widespread video surveillance (from body worn cameras, smart phones, and closed-circuit televisions) and its democratized channels of distribution (through social media). In this new environment, police misconduct (including perjury to protect a colleague) comes with the sizable risk of exposure and penalty. In addition, there’s a well-documented ratchet effect at work: select video footage of police misconduct inevitably goes “viral” and triggers structural reforms by a host of former allies, including internal affairs branches, city councils, and legislatures. This raises compelling doctrinal questions for criminal and constitutional law. Take, for instance, the “exclusionary rule.” A hallmark of the U.S. criminal justice system, the exclusionary rule provides generally (subject to various exceptions) that evidence gained in violation of the U.S. Constitution is inadmissible in criminal prosecutions. This long-standing rule will certainly be affected by enhanced transparency in policing. In the immediate future, criminal defendants will benefit most, as video footage (and fewer instances of officer perjury) will make it easier for them to prove constitutional violations. But in the long run, the government should reap the larger gains. The exclusionary rule imposes costs on society, which are justified only insomuch as the threat of suppression deters police misconduct. But what if police are sufficiently deterred by factors besides the fear of suppression? What if the proverbial bad cop is already suspicious, alienated, and excessively cautious? Is the exclusionary rule still justified? Because the marginal deterrent value of exclusion weakens as alternative deterrents gain strength, transparency in policing may well lead the U.S. Supreme Court to further winnow (or perhaps altogether abandon) the rule. This essay describes the rising transparency in policing and explores its ramifications for the exclusionary rule.

Optimal nonlinear taxation of income and savings without commitment

AbstractWhen a government is unable to commit to its future tax policies, information about taxpayers' characteristics revealed by their behavior may be used to extract more taxes from them in the future. We examine the implications of this ratchet effect for the design of redistributive income and savings tax policies in a two‐period model with two types of individuals who only differ in their skill levels. When commitment is not possible, it may be optimal to separate, pool, or partially pool different types in period one. The nature of the distortions to labor supplies and savings are investigated for each of these three regimes. The identification of the optimal regime is investigated numerically.

Complex dynamics from simple cognition: The primary ratchet effect in animal culture.

It is often observed that human culture, unlike most other animal culture, is cumulative: human technology and behavior is more complex than any individual could invent in their own lifetime. Cumulative culture is often explained by appeal to a combination of high-fidelity social learning and innovation, the “ratchet effect.” What is often overlooked is that both human and other animal culture is supported by a more primary ratchet effect that retains and increases the prevalence of adaptive behavior. This primary ratchet can arise without appeal to specialized cognitive adaptations and is plausibly more widespread in animal societies. We use a simple model to highlight how simple forms of contingent social learning can create the primary ratchet effect, dramatically increasing the prevalence of adaptive, hard to invent behavior. We investigate some ways that demography may interact with the primary ratchet to generate patterns of cultural variation. As the primary ratchet may be common to many animal societies, its cognitive components and population dynamics provide a common foundation for the study of animal culture and a necessary foundation for understanding the origins of human cumulative culture.

Young children fail to generate an additive ratchet effect in an open-ended construction task.

The ratchet effect–the gradual accumulation of changes within a cultural trait beyond a level that individuals can achieve on their own–arguably rests on two key cognitive abilities: high-fidelity social learning and innovation. Researchers have started to simulate the ratchet effect in the laboratory to identify its underlying social learning mechanisms, but studies on the developmental origins of the ratchet effect remain sparse. We used the transmission chain method and a tower construction task that had previously been used with adults to investigate whether “generations” of children between 4 and 6 years were able to make a technological product that individual children could not yet achieve. 21 children in a baseline and 80 children in transmission chains (each consisting of 10 successive children) were asked to build something as tall as possible from plasticine and sticks. Children in the chains were presented with the constructions of the two preceding generations (endstate demonstration). Results showed that tower heights did not increase across the chains nor were they different from the height of baseline towers, demonstrating a lack of improvement in tower height. However, we found evidence for cultural lineages, i.e., construction styles: towers within chains were more similar to each other than to towers from different chains. Possible explanations for the findings and directions for future research are suggested.

Asset management with endogenous withdrawals under a drawdown constraint

Asset preservation is a major concern for foundations that are hostile to large wealth downfalls. Implications for optimal consumption and investment policies are explored in a dynamic setting where wealth is restrained from falling below a fraction of its all-time high. Risky investment regulates wealth growth and mitigates the ratchet effect of the constraint, and may decrease as wealth approaches its maximum. The correspondence found between habit formation over consumption and wealth ratcheting provides a rational explanation for the proliferation of capital protection oriented funds.

Ratchet Effect in Partially Gated Multifinger Field-Effect Transistors

Ratchet Effect in Partially Gated Multifinger Field-Effect Transistors